Six percent of all children with febrile seizures are at relatively high risk for later afebrile activity. A proposal is being developed for a clinical trial which will examine the efficacy and toxicity of chronic and short-term prophylaxis for this group of children. At present chronic prophylactic medication is recommended by several authors without available information as to the potential success or side effects of such medication. The Developmental Neurology Branch, the Epilepsy Branch, and the Office of Biometry and Field Studies have been working together on this ongoing project.